Devices for studying or treating acoustic phenomena



y 1969 JEAN"'CLAUDE LAFON ET AL 3,458,669

DEVICES FOR STUDYING OR TREATING ACOUSTIC PHENOMENA Filed A ri 19, 1965 2 Sheets-Sheet 1 uwe/vmRs Eanui. afioh.

Rich av; g m,%wmwmui ATTORNEYS 3,458,669 DEVICES FOR STUDYING R TREATING ACOUSTIC PHENGMENA Jean-Claude Lafon, Saint-Rambert-lIle-Barbe, and Marc Richard, Lyon, Rhone, France, assignors to Centre National de la Recherche Scientifique, Paris, France, a French Government administration Filed Apr. 19, 1965, Ser. No. 449,021 Claims riority, application France, Apr. 20, 1964, 971,552 Int. Cl. H04r 25/00 US. Cl. 179-107 1 Claim ABSTRACT OF THE DISCLOSURE An auditive prosthesis device which comprises in-cornbination: a microphone capabl of transforming sounds into electric signals; a system for ditferentiating'a portion of said signals; means for collecting the other portion of said signals before their differentiation and for sending said other portion to an earphone capable of transforming it into sounds; and means capable of preventing the transfer of said other portion to said earphone at the times when the amplitude of the corresponding differentiated signals exceeds a predetermined threshold.

The present invention relates to prosthesis devices, or hearing aids, which serve to replace defective portions of an ear. More particularly, the present invention relates to devices for studying or treating acoustic phenomena, these devices being arranged in such manner as to detect the importance of the sound impulses contained in these phenomena, in particular in order to determine'-and possibly to reducethe degree of noxiousness of said impulses for the ears of the hearers or again to set up electric terms representative of the acoustic sensations truly perceived by the hearers of said phenomena.

It consists chiefly in including in the devices in question a microphone for transforming noises into electric signals, a system for differentiating at least a portion of these signals, in particular that corresponding to the frequencies audible by the internal ear, the time constant of this system being for this purpose lower than ,6 of a second, means for determining the amplitude of the signals thus differentiated, and further, preferably, means for measuring the maximum intensity of the noises producing said differentiated signals. further including, in the devices in question, means for collecting a portion of the electric signals before their differentiation and sending them to a suitable exploitation element, such, preferably, as an auditive prosthesis earphone and means for preventing the transfer of said nonditferentiated portion of the electric signals to said exploitation element at the times where the amplitude of the corresponding differentiated signals exceeds a predetermined threshold, said last mentioned means preferably including a monostable multivibrator the threshold of operation of which corresponds to said amplitude threshold and the time constant of which ranges from V to of a second and a gate controlled by the output of this multivibrator and intended for the passage therethrough of said nondifferentiated portion of the electric signals.

Preferred embodiments of the invention will be herein- United States Patent 0 "ice after described with reference to the appended drawings, given merely by way of example, and in which:

FIG. 1 is a diagram showing the shape of the envelope curve of an impulse acoustic phenomenon;

FIG. 2 is a diagram representing the derivative or differential of this curve with respect to time which differential is to be evolved and exploited according to the present invention;

FIG. 3 is a diagram illustrating the utility of the knowledge of said differential according to the present invention;

FIG. 4 is a simplified electric diagram of a device according to the present invention;

FIG. 5 shows the characteristic of a particular bandpass filter included in this device;

FIG. 6 shows another simplified electric diagram of a device for studying acoustic phenomena according to the invention;

FIG. 7 is the simplified electric diagram of a modification of a portion of the diagram of FIG. 6;

FIG. 8 is a simplified electric diagram of a modification of a portion of the diagram of FIG. 7;

FIG. 9 is a simplified electric diagram of an auditive prosthesis device according to the present invention.

The present invention relates to devices for determining, and possibly reducing, the importance of the impulses in noises, especially concerning risks of cochlear injury resulting therefrom.

It will first be reminded that, up to the present time, in order to determine the degree of noxiousness of a noise, it was believed insufficient to measure the mean sound level thereof with a sonometer.

Now we have found that, in order to appreciate the danger of a noise for the human car, it is necessary to know not only the intensity of this noise but also the form thereof and more precisely the rate of establishment or rate of amplitude increase thereof.

As a matter of fact it was found that the auditive troubles that were detected were negligible in subjects which had been made to support for considerable times intensive but continuous and stable noises, such as white noises (that is to say noises all the components of which have the same energy) emitted by pneumatic rotary drilling machine in a tunnel in the way of boring, and that such troubles were on the contrary frequent and important in the case of subjects which had been made to undergo noises of the same spectral composition as the preceding ones and even less intensive than them, but very short, such as those produced by firearms in a shooting gallery.

From this observation it was deduced that auditive traumatisms depended essentially upon the rate of variation of the intensity i of the noises, when of course the maximum value of this intensity was sufficient.

In order to bring into evidence this rate of variation, according to the present invention, We evolve the derivative of said intensity i (plotted in ordinates in FIG. 1) with respect to time t (plotted in abscissas).

We thus obtain a quantity p' di/dt plotted in ordinates in FIG. 2, as a function of time plotted in abscissas, which gives the curve 2 of the differentiated signal. The maximum value p of this quantity p is equal to the maximum slope of the front portion of the corresponding noise impulse I (FIG. 1). This value p therefore represents the maximum rate of establishment of said noise, that is to say its degree of suddenness.

In the preferred embodiments, we measure not only this value p but also the maximum intensity I' of the corresponding noise The higher these two values p and i representing respectively the rate of establishment of the noise and its maximum intensity, the greater are the risks of auditive traumatism and even of cochlear injury.

It is easy to fabricate a curve 3 (FIG. 3) indicating, for every value of the maximum intensit I' (plotted for instance in ordinates) the value 17 (plotted in abscissas) beyond which the dangers of auditive traumatism are serious. This curve 3 divides the quadrant corresponding to the positive coordinates into two zones, to wit a lower zone I corresponding to the audible noises which are not dangerous and an upper zone II corresponding to noxious noises. The point of this curve where the abscissa is zero corresponds to the threshold s of noxiousness for a permanent and stable white noise (of an intensity of about 125 db); as for the ordinate s of the horizontal asymptote of this curve (of -a value of about 90 db), it corresponds to the threshold of noxiousness for a white noise the rate of establishment of which would be infinite.

It should be noted that the global intensity or energy of a noise may be considered at any time as the sum of two terms, to wit the kinetic energy and the potential energy, only the first one of which is a function of the rate di/dt. Now it seems that the active organs of the internal ear (ciliate cells carried by a membrane contained in the cochlea) are sensitive only to said kinetic energy. In this case, the differentiation above referred to permits of developing a term which varies in the same direction as the excitation of said active elements, which term can therefore represent an aspect of the sensation experienced by the ear when receiving corresponding acoustic phenomena.

It is possible simultaneously to develop a whole series of terms of this kind corresponding each to a relatively narrow range of frequencies, in such manner as to constitute a kind of artificial image of the real auditive sensations corresponding to a more or less complicated acoustic phenomenon, which has never been obtained correctly before the present invention and involves great advantages concerning in particular the study of the relation between sounds or noises and the sensation they produce and the reconstitution of said sounds or noises and/ or sensations.

In what follows, we will describe, with reference to FIGS. 4 to 9, embodiments of the invention relating to the study (for FIGS. 4 to 8) and the reduction (for FIG. 9) of the degree of noxiousness of noises on the ears of the hearers.

The embodiment of FIG. 4 comprises, mounted in series, a microphone 4 capable of transforming into electrical signals the noises it receives, a variable attenuator 5, which may be logarithmic, for adjusting the level of said signals to a suitable value which does not risk of saturating the circuits, and a bandpass or linear amplifier 6 adjustable in a continuous or discontinuous manner.

The output 17 of this amplifier is connected:

On the one hand to a measurement system 16 (such as an amplitude counter) capable of determining the value of the maximum intensities i of the acoustic signals to be studied.

On the other hand a differentiating system 7, for instance of the type comprising a resistor 8 and a capacitor 9, followed by a measurement system 18 (such as the combination of an amplifier and of an amplitude counter) capable of determining the value of the maximum intensities p of the differentiated signals issuing from system 7.

Of course, if the noises that are studied are identically repeated, it is possible to utilize only one measurement system and to make it to perform alternately the functions of systems 16 and 18, as diagrammatically indicated by the dotted lines 19. I

The passing band of amplifier 6, if it is a band-pass amplifier, corresponds in this case to the range, from 2000 to 4500 Hz., of the frequencies of the signals audible by the internal ear, that is to say capable of injuring the ciliate cells carried by the cochlea. As a matter of face these signals seem to be the cause of the most serious auditive troubles due to an injury of the cochlea.

I We have shown in FIG. 5 a characteristic of a suitable filtering process for said amplifier, giving the amplitude a (in decibels) of the sounds it lets pass as a function of the frequency f. The increasing slope of this characteristic on the low frequency side is 12 db per octave, its decreasing slope on the high frequency side being 18 db per octave and the amplitude of the sounds that are transmitted, corresponding tofrequencies ranging from 2000 to 4500 Hz., is constant with an approximation of :3 db.

In order to have the signals issuing from amplifier 6 correctly differentiated, the time constant of the differentiating system must be lower than one half of the time interval between two consecutive alternations of the oscillating signal at the highest frequency, that is to say lower than V9000 second or approximately 10*. seconds.

It may be advantageous to provide a possibility of adjustment of this time constant, for instance between 0.5.10- and 10 seconds in a continuous or discontinuous manner.

Knowing the values of p and i corresponding to give noise it is possible to deduce from the diagram of FIG. 3 whether this noise is dangerous or even whether it presents risks of cochlear injury. In the case of the affirmative it will of course be necessary to reduce the intensity and/or the suddenness of this noise and/or to take the necessary precautions in the case where this noise is reproduced.

The embodiment illustrated by FIG. 6 still comprises the above mentioned elements 4, 5, 6, 7, 16 and 18.

It further comprises:

0n the one hand a conventional sonometer 29 connected to output 17 and making it possible to measure the mean intensity of the acoustic signals that are studied, and

On the other hand a chain of elements for measuring the duration for which the intensity of a noise remains above a given threshold.

This chain comprises:

A threshold amplifier 30 which passes after amplification, only the electric signals of an amplitude higher than a given threshold which may be zero.

A gate 31 fed on the one hand by the output of this amplifier 30 and on the other hand by the pulses transmitted at regular intervals from a quartz oscillator 32 and suitably shaped by a circuit 33, and

A counting scale 34 fed from said gate as long as the amplitude of the electric signals applied to the input of amplifier 30 exceeds said threshold.

We have indicated in dotted lines at 35 a bandpass filter which can easily be inserted between on the one hand the output 17 of amplifier 6 and on the other hand counter 16 and differentiating circuit 7 in order to limit the measurement of quantities i and p to noises the frequencies of which are within a predetermined range of values (if amplifier 6 does not already perform this function).

In FIG. 7 we have diagrammatically indicated a modi fication of the elements of FIG. 6 located following the output 17 of amplifier 6.

According to this modification, instead of directly measuring i and m, we first differentiate the corresponding signals to perform the integration thereof subsequently, which permits the integration thereof subsequently, which permits of using apparatus which are often less expensive.

The chain of measurement of quantity i comprises, successively, a differentiating circuit 36, an amplifier 37,

5 an impedance adaptor 38 with a low output impedance, an integrating circuit comprising a rectifier 39 and a capacitor 40, and a voltmeter 41.

The chain for measuring p comprises the same elements, and, in addition, a second differentiating circuit 42 with an amplifier 43.

If the noises that are studied are repetitive it is possible to have only a single system of adaptation 38, integration 39, 40, and measurement 41 for both chains by branching at will the two complementary elements 42 and 43 on the first chain, for instance at the output 56 of the amplifier 37 (or at the input of circuit 36) by means of a mere switch, in the manner diagrammatically indicated by dotted line 44.

Otherwise, the second chain also comprises, as supposed in FIG. 7, its adaptator 45, its integrating system (rectifier 46 and capacitor 47) and its voltmeter 48.

In FIG. 8, we have disclosed a modification of the elements of FIG. 7 located following the output 56 of amplifier 37.

According to this modification the differentiated and amplified signals applied at 56 are detected at 49 and their positive portions serve to modulate in duration, in modulator 50, rectangular signals. These signals are generated in a device 51 from a quartz oscillator 52 through, successively, a shaping circuit 54 and a frequency divider 58. The duration modulated signals coming from 50 are then applied to one of the two inputs of an AND gate 53 the other input of which is fed with regular impulses at higher frequency coming from circuit 54. The impulses delivered by this gate proportionally to the durations defined by the above mentioned differentiated signals are subesquently counted in a counting scale 55. The values indicated by this scale then correspond to the integrals of the positive derivatives of the incoming signals that are considered and therefore to the maximum intensities of these signals.

Of course, such a system 49-55 may also be used instead of the elements 45, 48 of FIG. 7.

We may also use the quartz oscillator 32 and the shaping circuit 33 to constitute oscillator 52 and shaping circuit 54 respectively.

Of course many other useful elements may be added to those indicated in the simplified diagrams represented by the figures, for instance manually or automatically controlled counting switches, current collectors (such as 57 in FIG. 8) intended for an oscilloscope control for a recording either magnetic or not.

We will now describe, with reference to FIG. 9, an apparatus intended, not to study noises, but to treat them in such manner as to eliminate therefrom the components that are too sudden.

The improved prosthesis device, or hearing aid, diagrammatically disclosed by this FIG. 9 essentially comprises, as any prosthesis device, a microphone 20 intended to transform into electrical signals the noises it receives, an amplifier 21 for said electrical signal and an earphone 22 capable of transforming into sounds the electric signals thus amplified.

We interpose between amplifier 21 and earphone 22 a delay unit 23 and a gate element 24.

This gate acts as a switch responsive to the rate of establishment of the noises acting upon microphone 20.

For this purpose, a portion of the electrical signals issuing from amplifier 21 is applied to a differentiating and detecting circuit 25. The signals thus differentiated control a threshold monostable multivibrator 26, the threshold of which is predetermined in accordance with the value of the derivative from which it is desired to block the connection between amplifier 21 and earphone 22. Every time this derivative exceeds this threshold, multivibrator 26 closes gate 24 for a predetermined time defined by the time constant of the multivibrator.

This duration generally ranges from and of a second and preferably is of the order of A of a second. As a matter of fact, an interruption of a duration lower than $4 of a second would be practically inoperative whereas a duration of interruption higher than & of a second would lead to a reduction of the intelligibility of the sound message.

The rate of reopening of the gate should be lower than the maximum admissible rate of establishment of the noises so as to avoid that sound impulses of long duration (that is to say of a duration longer than that defined in the preceding paragraph) are applied too suddenly to the hearer when such a reopening occurs.

The function of the micro-delay device 23 is to synchronize the two inputs of gate 24 corresponding to the same sound impulse.

The arrangement that is obtained permits of automatically suppressing from the signals transmitted to earphone 22 the components corresponding to sound impulses that are too sudden or at least to the periods of establishment of these impulses, which has the double advantage of making audition more agreeable and more intelligible.

It should be noted that the elements 23 to 26 added to the conventional prosthesis device 20-22 do not lead to a substantial increase of the volume of this device, the number of the components of these elements being reduced and there will be no difficulty in making them as small as necessary.

Earphone 22 may be replaced by any other exploitation element such for instance as a recording element.

Of course amplifier 6, instead of being provided for studying the noxious influence of noises on the ears, might be provided for studying the sensations produced by some sounds or noises, its curves of response being then chosen among those normally produced in the art of sonometry, the shifting of the amplifier to the desired function being advantageously obtained by a mere switch.

The output of the microphone might be connected simultaneously, or successively through any means for repeating the signals elaborated at said output) to a plurality of distinct channels each arranged in such manner as to treat the noises corresponding to a rather narrow range of frequencies, the whole of the :ranges of these different channels covering a portion of the whole of the spectrum of audible frequencies.

We might also take into account not only the rate of establishment of an impulsional noise but also its rate of disappearance and, in this case, use will be made of the negative ordinate portion of the differential signal 2 (FIG. 2).

In a general manner, while we have in the above description disclosed What we deem to be practical and efficient embodiments of the present invention, it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the appended claim.

What we claim is:

1. An auditive prosthesis device which comprises in combination: a microphone capable of transforming sounds into electric signals; a system for differentiating a portion of said signals, said differentiating system having a time constant lower than fl of a second; means for collecting the other portion of said signals before their differentiation and for sending said other portion to an earphone capable of transforming it into sounds; and means capable of preventing the transfer of said other portion to said earphone at the times when the amplitude of the corresponding differentiated signals exceeds a predetermined threshold, said preventing means comprising a monostable multivibrator the threshold of operation of which corresponds to the predetermined amplitude threshold of the differentiated signals and the time constant of which ranges from i to of a second, and a gate controlled by the output of said multivibrator and traversed by said other not differentiated portion.

References Cited UNITED STATES PATENTS 2,250,144 7/1941 Welty 375478 3,126,449 3/1964 Shirman 179-1.8 3,140,446 7/1964 Myers et a1. 325--324 XR KATHLEEN H. CLAFFY, Primary Examiner ROBERT P. TAYLOR, Assistant Examiner US. Cl. X.R.

P0405) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,458, 669 Dated July 29, 1969 Inventor) Jean-Claude Lafon and Marc Richard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Column 1, after line 48, insert A second feature of the present invention consists in SEALED a c" Q.

(SEAL) Amt:

WILLIAM E. susu mm, JR.

Attesting Officer Oommissioner of Patents 

